What is epistasis?

Epistasis refers to the phenomenon where the effect of one gene is modified or completely masked by one or more other genes. This means that the expression of a particular trait governed by one gene can be significantly influenced by the presence or absence of alleles at another gene locus.

For instance, consider a scenario where one gene determines pigment color in a plant and another gene controls the ability to produce that pigment. If the second gene is 'inactive' or non-functional, it does not matter what alleles are present for the first gene; the plant will not express the pigment color. This interrelationship is crucial to understanding inheritance patterns because it can complicate expected Mendelian ratios and lead to more complex traits being expressed in organisms.

In this context, the other options do not accurately capture the concept of epistasis. The interaction between multiple alleles pertains more to codominance or incomplete dominance. Nondisjunction pertains to chromosome separation errors during meiosis and is unrelated to gene interaction. Random distribution of chromosomes describes the independent assortment principle and also does not involve the intricate relationship between different genes that characterizes epistasis.